Response of a human head/neck/upper-torso replica to dynamic loading--I. Physical model

A human head/neck/upper-torso replica was constructed and instrumented and its response to impact and dynamic loading was studied. The model consists of a water-filled cadaver skull; plastic vertebrae, sternum and ribs; silicon rubber disks and ligaments; and fabric muscles. The static behavior of the system under sagittal plane and lateral loading was adjusted so as to correspond to that of cadaver behavior under similar loading. The structure was loaded impulsively by the sudden arrest of a supporting sled running on a track and by direct head impact with a suspended steel ball. The measured response included the head acceleration, the disk pressures, the muscle strains, the intracranial pressures and the skull strains; the sled motion was also monitored. These data were recorded with a microcomputer and oscilloscopes; the overall system deformation was observed by high-speed cameras. The muscle contraction effects were determined with the aid of microcomputer-controlled devices including a vacuum system, solenoid valves and plastic syringes.     

鄂中一些被子植物硅化木研究

本文研究了我国首次在长江北岸,湖北省新洲县发现的新生代晚第三纪大戟科、豆科和樟科的被子植物硅化木。这些硅化木的发现和鉴定,反映了该地区当时较为炎热潮湿的气候环境,并为长江流域新生代的地质、古气候、古地理、古生物群演变等方面的研究,提供了论据。     

青藏高原地区的光质对高原春小麦生长发育、光合速率和干物质含量影响的研究

本文模拟研究了高原地区的不同光质对春小麦的生长发育、光合速率和干物质含量等方面的影响。实验结果表明:(1)蓝光和蓝紫光的照射能使春小麦植株趋于矮壮。提高总叶绿素含量,增加叶绿素b值,并能延迟春小麦的生育期和干物质积累的时间。(2)红光和蓝紫光对春小麦品种的光合速率都比对照有提高效应,其中红光最显著,蓝紫光次之,而蓝光下最低。(3)红光和蓝紫光下积累的干物质含量均大于对照,蓝光下的较低。从而论证了青藏高原地区较好的光质,尤其丰富的蓝紫光是高原春小麦屡出高产的重要生态因素之一。为在这一地区充分利用这一得天独厚的有利条件挖掘更大的高产潜力提供了科学依据。     

柚花头香化学成分的研究(一)

本文首次报道柚花的香气成分。作者利用憎水性树脂XAD-4吸附柚鲜花的头香,并以毛细管气相色谱和毛细管气相色谱-质谱-计算机联用方法研究头香的化学组分,分离鉴定了17个已知化学成分。它们是芳樟醇、β-蒎烯、β-水芹烯、橙花叔醇等。     

Tungstate, a molybdate analog inactivating nitrate reductase, deregulates the expression of the nitrate reductase structural gene

Nitrate reductase (NR, EC 1.6.6.1) from higher plants is a homodimeric enzyme carrying a molybdenum cofactor at the catalytic site. Tungsten can be substituted for molybdenum in the cofactor structure, resulting in an inactive enzyme. When nitratefed Nicotiana tabacum plants were grown on a nutrient solution in which tungstate was substituted for molybdate, NR activity in the leaves decreased to a very low level within 24 hours while NR protein accumulated progressively to a level severalfold higher than the control after 6 days. NR mRNA level in molybdate-grown plants exhibited a considerable day-night fluctuation. However, when plants were treated with tungstate, NR mRNA level remained very high. NR activity and protein increased over a 24-hour period when nitrate was added back to N-starved molybdate-grown plants. NR mRNA level increased markedly during the first 2 hours and then decreased. In the presence of tungstate, however, the induction of NR activity by nitrate was totally abolished while high levels of NR protein and mRNA were both induced, and the high level of NR mRNA was maintained over a 10-hour period. These results suggest that the substitution of tungsten for molybdenum in NR complex leads to an overexpression of the NR structural gene. Possible mechanisms involved in this deregulation are discussed.     

Some physicochemical properties of rice mitochondrial DNA

Summary Certain physicochemical properties of rice mitochondrial DNA (mtDNA) were determined. Certain low-molecular-weight mtDNA bands were found in addition to the major mtDNA band. Rice mtDNA appeared in the electron microscope as a collection of linear molecules with heterogeneous length in the range of 1–156 kb. The major distribution area was 60–105 kb. A small fraction (less than 5%) of rice mtDNA was found in the form of a circular molecule. Some molecules had the appearance of being supercoiled. Replication fork structures were found in both circular and linear mtDNA molecules. In one rice species, Jin Nante, 15 different circular molecules were found. Rice mtDNA was digested with different restriction enzymes. The total molecular weight of rice mtDNA was calculated to be about 300 kb according to the data of restriction enzyme digestion and electron microscopy.     

Homologous plasmid recombination is elevated in immortally transformed cells.

The levels of intramolecular plasmid recombination, following transfection of a plasmid substrate for homologous recombination into normal and immortally transformed cells, have been examined by two independent assays. In the first assay, recovered plasmid was tested for DNA rearrangements which regenerate a functional neomycin resistance gene from two overlapping fragments. Following transformation of bacteria, frequencies of recombinationlike events were determined from the ratio of neomycin-resistant (recombinant) colonies to ampicillin-resistant colonies (indicating total plasmid recovery). Such events, yielding predominantly deletions between the directly repeated sequences, were substantially more frequent in five immortal cell lines than in any of three normal diploid cell strains tested. Effects of plasmid replication or interaction with T antigen and of bacterially mediated rejoining of linear molecules generated in mammalian cells were excluded by appropriate controls. The second assay used limited coamplification of a control segment of plasmid DNA, and of the predicted recombinant DNA region, primed by two sets of flanking oligonucleotides. Each amplified band was quantitated by reference to a near-linear standard curve generated concurrently, and recombination frequencies were determined from the ratio of recombinant/control DNA regions. The results confirmed that recombinant DNA structures were generated within human cells at direct repeats in the transfected plasmid and were markedly more abundant in an immortal cell line than in the diploid normal cells from which that line was derived.     

Scavenging effect of extracts of green tea and natural antioxidants on active oxygen radicals

With the use of the spin trapping methods, the scavenging effects of the extracts of green tea and other natural foods are studied. In stimulated polymorphonuclear leukocytes (PMN) system, water extract fraction 6 (F6) from green tea and green tea polyphenols (GTP) have the strongest scavenging effect on the active oxygen radicals, much stronger than vitamin C (Vc) and vitamin E (VE). Rosemary antioxidants (RA) and Curcumin (Cur) have weaker scavenging effects than Vc, but stronger than VE. In Fenton Reaction, Cur has the strongest scavenging effect (69%) on hydroxyl radicals. In irradiation, riboflavin system F6(74%) and GTP(72%) have very strong scavenging effects that are weaker than Vc, but much stronger than VE (23%). With the use of spin probe oxymetry, the oxygen consumption in respiratory burst of stimulated PMN were measured when the antioxidants existed in these systems. The results demonstrated that these antioxidants did not affect the respiratory burst of human polymorphonuclear leukocytes stimulated with PMA.